When designing a loudspeaker, especially a diaphragm of a speaker, it is most important that the diaphragm has high stiffness for reproducing audio signals with high fidelity, while it is also important that the diaphragm is light in weight and has moderate internal loss for obtaining high efficiency. Recently, a disk having a honeycomb construction draws attention since such a disk may be used as a core of a diaphragm, and a diaphragm comprising such a disk has a possibility to meet the above-mentioned requirements.
The above-mentioned disk having a honeycomb construction is manufactured by developing a multi-layer block constructed by a plurality of rectangular thin layers made of aluminum, titanium or the like. Namely, a multi-layer block having a rectangular prism shape is simply developed by pulling the both sides of the block to form a round disk which includes a number of hexagonal sections or cells. However, when developing such an undeveloped multi-layer block into a disk by the above-mentioned conventional manner, forces for restoring the original state of the multi-layer block occur therein, and the intensity of forces at the beginning of the development considerably differs from that of forces at the end of the development. As a result, the density of the hexagons developed at the end greatly differs from that of hexagons developed at the beginning. Namely, the density of the hexagons in the disk is not uniform throughout the circumference. For this reason, a conventional speaker diaphragm using such a disk having a honeycomb construction suffers from unflatness in the sound pressure level to frequency characteristic when used in a loudspeaker.